The invention relates to an apparatus and a method for monitoring a vascular access.
Specifically, though not exclusively, the invention can be usefully applied in detection of detachment of a needle in an extracorporeal blood circuit, such as for example an extracorporeal circuit used in a dialysis treatment.
The prior art comprises various systems for monitoring a needle, typically a needle (generally called a venous needle) via which extracorporeal blood is returned to the body of the individual.
Some known systems for detecting a detachment of the needle from the patient are based on detection of the presence of blood that has exited from the detached needle and/or the vascular access and spilled onto the patient's body. These systems can be based on a monitoring performed with a sensor of an electrical parameter (such as for example in US 2002/0198483, WO 99/24145, FR 2737124, U.S. Pat. No. 7,276,041), or an optical parameter (such as for example WO 2006/001759 and US 2006/0130591), or both (such as for example EP 1736185 and EP 1263488).
Other known systems (see for example U.S. Pat. No. 6,663,585, WO 02/102441, WO 01/47581, WO 03/086504, WO 2006/138359, US 2006/0081517, DE 102006041265) are based on monitoring the state of an electrical circuit formed at least partly by at least a tract of blood circuit, exploiting blood's characteristic of being electrically conductive.
A further known system is described in US 2007/0118064, in which an apparatus guides the blood in the venous line in an inverse direction, using an ultrafiltration pump, and detects a detachment of the venous needle on the basis of recognition of a presence of air bubbles in the venous line itself.
There also exist systems based on the monitoring of the pressure in the extracorporeal circuit, such as for example U.S. Pat. No. 4,898,576, EP 328162, US 2005/0010118, U.S. Pat. No. 6,077,443, U.S. Pat. No. 6,221,040, WO 03/002174, U.S. Pat. No. 6,090,048.
U.S. Pat. No. 4,898,576 describes an infusion system in which the infusion flow has a periodic variation and in which the state of the vascular axis is determined on the basis of the flow resistance, which is calculated on the basis of the variation in pressure in relation to the flow variation.
EP 328162 describes an infusion system in which the pressure signal measured in the infusion line downstream of the infusion pump is filtered by a high-pass filter and the filtered signal is evaluated in order to calculate the correct communication with the vascular access.
US 2005/0010118 describes a dialysis apparatus in which the disconnection of the needle from the vascular access is detected when the frequency component, caused by the heartbeat of the patient, disappears from the pressure signal measured in the extracorporeal circuit.
U.S. Pat. No. 6,077,443 shows a dialysis apparatus in which a series of pressure pulses are generated in the dialysis circuit and the detachment of the needle is detected by the monitoring of the pressure pulses induced in the extracorporeal blood circuit of the series of pulses.
U.S. Pat. No. 6,221,040 shows a dialysis apparatus in which the detachment of the venous needle is detected by analyzing both the venous pressure and the arterial pressure of the extracorporeal circuit.
WO 03/002174 describes a dialysis apparatus in which the detachment of the venous needle is detected if both the venous pressure and the arterial pressure are reduced and, during the same period of time, the extracorporeal blood flow stays constant.
U.S. Pat. No. 6,090,048 describes a dialysis apparatus in which the detachment of the venous needle from the patient is determined by verifying whether a pressure wave, generated by the blood pump or the heartbeat, passes through the needle and reaches the pressure sensor on the venous line.
The prior art also comprises WO 2007/033025 which describes an apparatus infusion control in which the infusion fluid flow rate is controlled in response to patient parameter values measured, such as for example pulse oximetry and blood pressure.